Reply to ASK-AN-EARTH-SCIENTIST

Subject: Acid Rain in Oregon

How much acid rain falls yearly in Oregon?
Where does the pollutant that forms acid rain come from?
What kind of destruction can/does acid rain cause?
How long do the affects of acid rain last?
Do you think we will ever be rid of acid rain?
How is acid rain formed?
What are the affects of acid rain on animals?
And the foods that they eat? Ex. grass
How does it affect the rivers and lakes and the animals in them?
What do you think the affects of acid rain will have done to the
earth in 20 years?
Do you think we are cutting down on sulfer oxide to reduce acid rain or
are we using more?

Where does the pollutant that forms acid rain come from?
How is acid rain formed?
Acid rain forms when molecules of oxidized sulfur and/or nitrogen in
the atmosphere combine with water, forming acidic compounds that
dissolve in the water that becomes rain. Typical sulfur compounds
(SO2 ans SO3) get into the atmosphere from both natural (i.e. volcanoes,
windblown dust containing gypsum-which has SO4 ions in it, etc..) and
non-natural (i.e., burning of coal, refining of metal ores) sources.
Nitrogen compounds also get into the
atmosphere and form acids, although the natural sources are much more
limited. The biggest non-natural source is buring fossil fuels,
especially gasoline.

How much acid rain falls yearly in Oregon?
This is difficult to quantify, since it depends on how acidic the
rain is (e.g., how low the pH is) and how much it rains. Both
parameters vary widely over the state of Oregon. In general, Oregon
rain is only mildly acidic. Rain there has typical pH values of 5.2
to 5.4. By contrast, parts of the North Eastern US and Southern
California have rain with pH values of 4.2 to 4.8. By comparison,
natural rainwater has it's pH controlled by the CO2 that is dissolved
in it, and is buffered at a pH of about 5.7. Remember, neutral pH =7
(no acidity or basicity) and acidity increases as pH goes down.
Much of the acid rain
in the Pacific Northwest is from natural (mostly volcanic) sources. In
the North East, the sulfur in the atmosphere is mostly non-natural. In
parts of the desert west and in Hawaii, there is a large amount of natural
sulfur put into the atmosphere.
Acidic rain and fog in western US metropolitan areas
such as L.A. is mostly caused by HNO3 (nitric acid), due
to all of the automobile exhaust. Acid rain in the north east is mostly
H2SO4 (sulfuric acid) from all of the coal buring that goes on there. In
Hawaii, Kilauea volcano puts sulfur into the atmosphere and makes natural
acid rain. There is also a small amount of natural hydrochloric acid (HCl)
put into the atmosphere this way. Fortunately, our abundant rain and winds
dilute the acid in the rain and mostly blow it out to sea, although a
large desert area exists in one area of otherwise-lush Kilauea volcano due
to acid fallout.

What kind of destruction can/does acid rain cause?
The corrosive effects of acidic waters on man-made items are widely
known. On the other hand, we only can speak mostly in generalities
when discussing the effects of acid-rain on natural environments.
The short-term danger from acid rain is mostly to forest and
lake ecosystems, which
are very sensitive to chemical imbalances in their environment. With the
loss of these ecosystems that effectively moderate the pH of surface
run-off water in many areas, the effect of acid rain on local water
supplies could become more pronounced in the future.

What are the affects of acid rain on animals? And the foods that
they eat? Ex. grass
How does it affect the rivers and lakes and the animals in them?
All organisms have certain tolerances for a range of pH values in
the environments in which they live. Some, in fact, only like
fairly acidic environments. In general however, low pH (acid)
waters are harmful to most land and water plants, severely stunting
their growth or even killing them. this in turn affects all other
animals further up the food chain due to lack of food and shelter.
Rivers and lakes are particularly fragile, because changing the pH
changes the balance of materials that are dissolved in the waters
versus those that are sedimented to the bottom of these bodies.
High acidity can alter (both increase and decrease) the concentration
of nutrients and poisons in natural waters, upsetting the natural cycle
by this change in chemical makeup.

Do you think we will ever be rid of acid rain?
No, because the natural sources are not dimishing. Anthropogenic sources
may dimish in the future, since the technology to reduce acid
emissions exists today. The question is: are we willing to pay more for
goods and services to help offset the cost of their use?

Do you think we are cutting down on sulfer oxide to reduce acid rain or
are we using more?
This is a tough question, because while some nations are cutting back
on acid emissions, others are actually increasing them. I don't know
for sure but my sense is globally we have not seen a significant
reduction in the man-made sources of acid emissions.